Modern voice messaging systems utilize several techniques to achieve transmission efficiency. Overlap-add time compression of speech is one such technique. This technique works well up to a compression ratio of about 2.5:1. Of course, service providers would like to be able to achieve even higher compression to further improve transmission efficiency.
A limitation of prior art voice messaging systems has been that voiced speech, unvoiced speech, and silence (i.e., pauses in speech) are processed exactly the same. This does not achieve maximum transmission efficiency, because silence, which contains very little information, can be compressed much more than 2.5:1 with little impact on voice quality.
Thus, what is needed is a method and apparatus that can achieve a greater compression ratio for speech pauses. Preferably, the method and apparatus will accomplish this in a manner that restores the pauses during message playback so that the rhythm of the message remains natural.